This invention relates generally to sticker placer apparatus. More particularly, this invention concerns improved apparatus providing inclined sticker feed pockets, positive sticker capture throughout placement, and a drive linkage that permits each placement arm in a system to `seek` the level of the top of the course of lumber. The combined features of the invention provide sticker placer apparatus achieving accurate placement and high throughput in virtually jam-proof, fully automatic operation.
Sticker placer apparatus are used to place stickers between stacked courses of fresh-cut lumber. The sticker serves the purpose of stabilizing the stacked lumber and permitting airflow between courses while the lumber cures. Typically, sticker placer apparatus are used in conjunction with lumber stacking equipment, wherein the lumber stacker develops a course of lumber and then the sticker placer places stickers transversely therealong above which the lumber stacker develops another course, etc. The number of sticker placement positions within a sticker placer is dependent upon the maximum course length and required spacing between stickers. Most multistation sticker placers operate the various positions simultaneously, wherein a number of stickers are placed in spaced apart relationship with one another along the length of the course of lumber.
A number of problems attend the use of conventional sticker placer apparatus. Most have to do with the imperfections frequently found in the stickers themselves, which are manufactured cheaply and are continuously recycled. With normal use, stickers tend to bow, twist, crook, wear and flatten as a result of being pressed between courses of lumber of varying thickness, and as a result of handling and weathering. In some cases, the thinnest sticker approaches half the thickness of the thickest sticker. Stickers also may be oversized in thickness from improper manufacture, or may be of varying surface conditions from improper screening or grading.
Conventional sticker placer apparatus store stickers in sticker feed pockets, or magazines, one atop the other with the greater cross-sectional dimension oriented horizontally. In order to eject or release the bottom sticker in a feed pocket, conventional placers either pinch the edge of the second sticker from the bottom of the pocket, while permitting the bottom sticker to drop free, or provide a throat, in the side of the pocket's base, large enough for a single sticker to be ejected sideways through, yet small enough to prevent the ejection of more than one.
The former type of sticker placer, commonly known as a pinching sticker placer, suffers the drawback that the second sticker from the bottom precisely must be located and shaped in the area of the pinching mechanism to prevent its falling. Thus, if the second sticker is too high or too low because the bottom sticker is too thick, too thin, twisted or bowed, the pinching mechanism cannot pinch it properly and keep it from falling. Similarly, if the edge of the second sticker is not both planar and vertical in the area of the pinching mechanism, the mechanism may be incapable of preventing its falling.
The latter type of sticker placer, commonly known as a side ejection sticker placer, easily may jam when two thin stickers find their way to the bottom of the feed pocket and both attempt to pass simultaneously through the opening. Similarly, if the bottom sticker is oversized in thickness or twisted or bowed, it may not pass through the opening. Finally, the surface condition of one or both of the bottom stickers in the feed pocket may prevent their sliding smoothly across one another, resulting thereby in a jammed sticker placer.
Other problems arise when a conventional sticker placer is used with courses of lumber that, when stacked, are uneven (nonplanar) or unlevel. Typically, a multi-station sticker placer positively links together the reciprocating motion of its placement arms. All arms descend for a predetermined period of time or until the earliest stop is reached, and then all arms simultaneously halt their descent, regardless of whether all arms have reached the level of the top of the course of lumber. As all stickers then are released simultaneously, some therefore are not controllably placed, but rather are dropped onto the course of lumber. Furthermore, if one arm of a multi-position sticker placer should jam, none is allowed to operate, because the movement of the common link mechanism is stopped. Similar problems arise with those side ejection sticker placers that eject stickers from multiple positions simultaneously through a positive link drive. Once again, if an individual sticker ejector jams, the movement of the common link is stopped, and none of the stickers is ejected.
It is desirable to provide an improved sticker placer that overcomes the problems described above. Specifically, the sticker placer should be highly tolerant of the inevitable sticker misfits, and should be virtually jam-proof. Such a sticker placer would be capable of fully automatic, repeatably accurate and rapid placement of multiple stickers atop consecutive courses of lumber, which may be not precisely level or planar. The improved sticker placer should operate reliably under extreme environmental conditions of dust and humidity.
Accordingly, it is a principal object of the present invention to provide a multi-position sticker placer having significantly improved placement accuracy, throughput and reliability.
Another object of the invention is to provide such apparatus that is compatible with automatic loading of the sticker feed pockets.
Yet another object of the present invention is to provide a sticker placer that optimizes the path traversed by a sticker between horizontal conveyance and vertical placement.
A further object of the invention is to provide a virtually jam-proof, multi-position sticker placer.
Still another object of the invention is to provide such apparatus with a minimum number of drive mechanisms.
Another important object is to provide multi-position apparatus that permits the selective disabling of individual
The apparatus of the present invention takes the form of a stationary, frame-mounted apparatus including multiple, gravity-fed inclined sticker feed pockets, each of which feeds edge-abutted stickers to a vertically reciprocable placement arm. Selectively, each placement arm alternately may be lowered and raised by a slider link, or roller chain, that adjustably is extended and retracted by a single, hydraulic or pneumatic cylinder common to all arms. It will be understood that slider link, as used herein, describes the fact that the link is permitted to slip, or disengage individual arms from the common drive cylinder during the extension thereof, thus distinguishing positive links that rigidly connect members for one-to-one movement therebetween.
Each placement arm is equipped with dual, positive sticker capture means including a pivotable, generally horizontal cradle and releasable sticker retaining means, which impinge, throughout the placement cycle, on the sticker's upper face. Plural stops halt each arm's descent when the top of the lumber course is reached thereby, causing the roller chain to slacken until fully extended. The resulting lost motion beneficially provides a dwell time during which a spring tensioned rocker arm, to which the roller chain is attached, may pivot the support arm out from under the sticker. During this dwell time, the sticker retaining means continues to urge the sticker downwardly, thus accurately and securely positioning it atop the course of lumber. Pivoting of the rocker arm, made possible by the slackening of the roller chain when at least one of the placement arm's stops reaches the top of the lumber course, also positions the roller chain on the opposite side of the rocker arm's pivotal axis so that, upon retraction of the roller chain, the support arm is maintained in its pivoted, sticker releasing position as the placement arm is raised and the placement cycle is completed.
The to-be-placed sticker immediately upstream from the sticker being placed is retained, throughout the placement cycle just described, by an adjustable, spring tensioned pinch bar that impinges upon the to-be-placed sticker's upper face until the placement arm completes its upstroke. Thus, by the orientation of the stickers in edge, rather than face abutment, and by the positive retention of upstream stickers within the feed pocket, stickers smoothly, controllably advance toward the placement arm.
Feed gates are provided adjacent the top of each feed pocket. Controlled opening and closing of the feed gates and the use of a conventional conveyor, preferably loading chains, provide uninterrupted, fully automatic operation of the sticker placer apparatus.
Thus, the objects of the invention are realized. Stickers are handled within the inclined feed pocket in edge-to-edge, rather than face-to-face, orientation, which renders them more controllable despite surface irregularities, over- or under-sizing, bowing, twisting or crooking. By the positive capture of each sticker by its opposing faces, rather than opposing edges, placement accuracy is greatly improved. Inherently unreliable timing circuits and limit switches are avoided by the use of placement arm-mounted stops, spring tensioned rotation and a slider link, which provide dwell time between the down- and up-strokes for the time-critical release of the sticker. Lost motion provided by the stops, the variable tension slider link and the common drive cylinder enable each placement arm to `float` to the level of the lumber at its position along the length of the lumber course, and permit other placement arms to continue to operate in the event one or more jams. A selectively operable feed gate at the top of each feed pocket provides an uninterrupted supply of stickers, based upon the demand at each placement position, for the fully automatic operation of the sticker placer.
These and other objects and advantages of the invention will become more fully apparent when the detailed description below is read with reference to the accompanying drawings.